VLA-4 (“very late antigen-4”; CD49d/CD29; or α4β1) is an integrin expressed on all leukocytes, except platelets and mature neutrophils, including dendritic cells and macrophage-like cells and is a key mediator of the cell-cell and cell-matrix interactions of these cell types. The ligands for VLA-4 include vascular cell adhesion molecule-1 (VCAM-1), the CS-1 domain of fibronectin (FN), and the matrix protein, osteopontin. Neutralizing anti-α4 antibodies or blocking peptides that inhibit the interaction between VLA-4 and its ligands have been shown to be efficacious both prophylactically and therapeutically in several animal models of disease including asthma, multiple sclerosis, inflammatory bowel disease, and rheumatoid arthritis.
The humanized monoclonal antibody against α4, natalizumab (Antegren®, Elan/Biogen), has demonstrated efficacy in the treatment of multiple sclerosis (D. H. Miller et al., New England Journal of Medicine, 348, 15 (2003)) and Crohn's disease (S. Ghosh et al. New England Journal of Medicine, 348, 23 (2003)). There are also several VLA-4 antagonists in early clinical trials for treatment of asthma, arthritis, multiple sclerosis, and Crohn's disease.
In the early clinical trials with natalizumab, lymphocytosis (a surrogate marker for blockade of VLA-4 function) and >80% receptor occupancy were observed. A small molecule VLA-4 antagonist was reported to demonstrate functional activity in the rat experimental autoimmune encephalomyelitis (EAE) assay, an animal model of multiple sclerosis following subcutaneous administration (D. R. Leone et al., J. Pharmacol. Exper. Therap., 305, 1150 (2003). This compound was shown to induce lymphocytosis, and to have a slow dissociation rate (off-rate) resulting in significant and sustained receptor occupancy on VLA-4-bearing cells. There was a positive correlation between receptor occupancy, lymphocytosis, and efficacy in the EAE model described in this manuscript.
A series of isonicotinoyl-L-aminophenylalanine derivatives shown to possess slow dissociation (off-rate) from VLA-4 on Jurkat cells were reported in G. Doherty et al., Bioorganic & Medicinal Chemistry Letters, 13, 1891 (2003). However, the compound that was further characterized demonstrated very poor pharmacokinetic properties such as low oral bioavailability, moderate to high plasma clearance and a short half-life rendering it unsuitable for oral administration. Compounds of the present invention are potent antagonists of VLA-4 capable of achieving and maintaining receptor occupancy for a time sufficient to allow for oral administration.